Nuclear magnetic resonance imaging is utilized for scanning and imaging biological tissue as a diagnostic aid. A conventional MRI apparatus includes a primary magnet, an RF generator, and a detector. The magnetic field produced by the magnet and the RF field produced by the RF generator are applied to the subject tissue, and the resulting nuclear magnetic resonance is read by the detector. The NMR data is then processed to produce an image of the tissue.
The RF signal used in MRI is commonly produced by a transmitter coil. The conventional saddle-shaped MRI transmitter coil interferes with the useable imaging volume and makes it difficult to administer certain applications within the imaging volume. Further, the conventional transmitter coil produces a non-uniform RF field.
Newer, open-gap transmitters eliminate these problems, but further development and improvement is desirable to overcome other disadvantages in the open-gap design. For example, large coils are utilized to generate the RF field, and only a small part of the spatially extensive transmitter generates the field in the correct direction and magnitude in the scanning volume located in the center of the magnet gap. Thus, due to the inefficient design, a large percentage of the RF power is dissipated elsewhere. Also, because these transmitters generate linearly polarized fields, one-half of the generated power is lost, another source of inefficiency. The large coil size also results in the generation of high voltages, which causes discharge and arcing problems.